A hologram is a recording of a light field emitted from a holographed object, e.g., a three-dimensional (3D) photographic scene, and is used to display a holographic image of that subject. Specifically, a hologram is an encoding of the light field as an interference pattern of variations in the opacity, density, and surface profile of the holographed subject. When suitably lit, the interference pattern diffracts into a reproduction of the original light field, so that the holographed subject appears to still be there, exhibiting visual depth cues, such as parallax and perspective, that change realistically with any change in the relative position of the observer (e.g., various viewing angles).
Displaying high quality holographic images in an efficient and accurate manner is difficult. For example, complex holograms comprise both amplitude information and phase information in an encoded light field, which are numerically represented by real components and imaginary components, respectively. These holograms, which record the complex wave front of the light field, are capable of reproducing excellent quality 3D holographic images. However, unless expensive and cumbersome steps are taken, available hologram display devices can only reproduce either amplitude information or phase information with a desirable degree of accuracy and efficiency.
One solution involves utilizing a pair of display devices to display a complex hologram by combining an amplitude hologram displayed by one device with a phase hologram displayed by another device. Another solution involves combining two phase holograms, each displayed by a respective device, to generate a “double phase” hologram. However, these solutions are difficult to implement because it requires a complicated set up and a precise optical alignment between the display devices, which can be tedious to realize in practice.
Other solutions involve utilizing a single display device in an attempt to display high quality holographic images, but these solutions are not satisfactory. For example, a single display device has been utilized to display a pair of holograms (i.e., an amplitude-only hologram and a phase-only hologram) and subsequently merge the reconstructed wave front through a grating. However, this requires complicated optics, high computation cost, and suffers from degraded image quality.
A single display device can also be utilized to display either an amplitude-only hologram or a phase-only hologram. If an amplitude-only display device is used, the resulting image is contaminated with a de-focused “twin image” unless additional, burdensome steps are taken to remove that image. Further, the optical efficiency of an amplitude-only hologram is typically low. If a phase-only display device is used, the resulting image may have higher optical efficiency, but is often subject to heavy distortion. Specifically, generating a pure phase hologram and displaying same with a phase-only display device typically suffers from limitations including high noise, complicated optics, high computational costs, additional processing requirements, low optical efficiency, and being confined to a small display area.
Another known solution involves generating a sampled-phase-only hologram, where an intensity profile of a holographed object is down-sampled to create sparse representation, i.e., a representation containing less information, of the intensity profile. A complex hologram is then generated from the sparse representation, and the phase value of the complex hologram is retained while the amplitude value is set at a constant value. This solution can produce acceptable visual quality of a reconstructed holographic image in some circumstances, but because the resulting image is sparse, it commonly suffers from holes or information gaps. This reduces overall holographic image quality.